A number of studies have examined the link between reduced sleep in children and increased risk of obesity. Now, a new study claims to be the most comprehensive one yet, offering "compelling evidence" that children who consistently had reduced sleep in early childhood went on to have increases in obesity, adiposity or overall body fat by age 7.

The researchers, from Massachusetts General Hospital for Children, publish their findings in the journal Pediatrics.

In 2006, a study published in the Archives of Disease in Childhood suggested that reduced sleep sets up a vicious circle where fatigue leads to reduced physical activity, which leads to lower energy expenditure, which leads to obesity, which leads back into poor sleeping patterns.

However, most of the previous studies on the subject had not examined the effects of constant sleep deprivation across time and had only measured obesity using body mass index (BMI). The new study drew its data from Project Viva, a long-term investigation of several factors that affect the health of children during pregnancy and after birth.

Lowest sleep scores reflected highest body measurements

Project Viva's data came from in-person interviews with mothers when their children were 6 months, 3 years and 7 years old, and from questionnaires the mothers completed when their children were 1, 2, 4, 5 and 6 years old.

The mothers were asked how much time their children spent sleeping, both at night and in the daytime. When the children were aged 7, the researchers also took measurements of height, weight, total body fat, abdominal fat, lean body mass and waist and hip circumferences. The researchers believed that these measurements would be a more accurate way of measuring cardiometabolic health risks than just measuring BMI.

Setting a consistent bedtime, limiting caffeinated beverages and cutting out high-tech distractions in the bedroom help promote good sleep habits.

As part of the study, each child was assigned a "sleep score" - from 0 to 13 - based on the mothers' reports.

The researchers found that the children with the lowest sleep scores had the highest levels of body measurements reflecting obesity and adiposity. This association was found to be consistent at all ages, so it does not seem there is a "critical period" when the interaction between sleep and weight has the greatest effect.

"Our study found convincing evidence that getting less than recommended amounts of sleep across early childhood is an independent and strong risk factor for obesity and adiposity," asserts lead author Dr. Elsie Taveras.

"Contrary to some published studies, we did not find a particular 'critical period' for the influence of sleep duration on weight gain. Instead, insufficient sleep at any time in early childhood had adverse effects."

Children from families with lower incomes or less maternal education - or who belonged to racial and ethnic minorities - had the lowest sleep scores. However, the researchers say that the association between sleep and obesity and adiposity was not changed when the findings were adjusted for these other factors.

Dr. Taveras says that more research is needed to establish how sleep duration affects body composition:

"While we need more trials to determine if improving sleep leads to reduced obesity, right now we can recommend that clinicians teach young patients and their parents ways to get a better night's sleep - including setting a consistent bedtime, limiting caffeinated beverages late in the day and cutting out high-tech distractions in the bedroom."

"All of these help promote good sleep habits," she adds, "which also may boost alertness for school or work, improve mood and enhance the overall quality of life."

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